1. Field of the Invention
The present invention relates in general to printed circuit boards and a method of manufacturing a printed circuit board. In particular, the present invention relates to a thin, flat, two-sided printed circuit board having openings in which components are mounted.
2. Description of the Related Art
High density printed circuit boards create greater utility in a smaller electronic device. Increasing the density of circuit components on a printed circuit board, however, often results in overheating of the components, leading to eventual burnout and replacement of the components. The resulting overheating can also cause higher stress and strain in the interconnects, such as solder joints, leading to an early failure. Moreover, the trend towards an increasingly compact product has resulted in increasing use of thinner and smaller printed circuit boards. Consequently, chips have decreased in thickness and are attached closer and closer to the printed circuit board.
Conventional methods of mounting circuit components on a printed circuit board include a "thorough-hole" technique which involves extending leads of a circuit component through the printed circuit board and then soldering the leads in place. The leads electrically connect circuit paths embedded on or within the board.
Another mounting method, known as "Surface Mount Technology" (SMT), involves initially placing circuit components onto circuit paths embedded on the upper surface of the printed circuit board and then soldering the component in place using a process called "reflow soldering." Surface mount components utilize connector leads commonly referred to as "J-leads" which rest on the surface of the printed circuit board rather than penetrate through it as with the through-hole technique.
The application of SMT increases the density of circuit components on a printed circuit board by enabling the use of smaller components which are arranged in a flat configuration on the surface of the board. In such surface mounted components, the leads to be mounted may be tightly spaced, as compared to components mounted by the thorough-hole technique, enabling increased access per unit area of the component. However, the resulting circuit board is still bulky, as the components extend from either surface of the board. In addition, in printed circuit boards manufactured using SMT, components occupy approximately 60% of the board, severely limiting routing connections. In contrast, in circuit boards designed for receiving dual-in-time packaging (DIP) components, typically only 19% of the board surface is covered by components, leaving ample room for routing connections.
Other current techniques of mounting circuit components include embedding chips into recesses in the board to further reduce the overall thickness of the board. However, such a technique suffers from several drawbacks. First, the chips are not firmly held in place. Second, the use of recesses for embedding the chips prevent two-sided wiring. Thirdly, only selected components are placed in these recesses, while the remaining components are surface mounted. This results in providing a printed circuit board that is still bulky.
Accordingly, there is a need in the technology for a method and apparatus of providing a printed wiring board that is cost-effective, thin, flat and strong. The printed wiring board must also provide two-sided wiring, high integrated component density and must also hold the components securely in place.